Why do we tend to value our own things more than they are worth?

I see this all of the time on eBay and Craiglist, that people set high reserve prices on things that they are selling. It could be an outdated iPod, or anything really, but sellers tend to set the starting bid very high, almost to the point that it seems like they don’t really want to sell it.

Is it sentimental value being compensated into the price, or is it something else?